In addition to the icons in the editor window toolbar being black with transparent background on a dark grey background, making it impossible to read them, spoiler text now seems to be having the same issue.
For example, this spoiler text is black on the standard backgorund, so even clicking on it fails to properly reveal the text.
Something is badly off in the CSS! Ah, here’s a likely looking culprit:
d-editor-button-bar button {
background-color: transparent;
Noooooooo!!!
Paging @discourse, @Jeffybug…